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    <script>
        var num=10;
        num++;//num=num+1
        console.log(num);
        // 前置自增跟后置自增单独使用是一样的，
        // 后置自增 口诀：先返回原值 后自加1
        var num=10;
        console.log(num++ +10);//20
        console.log(num);//11
    </script>
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